This invention relates to an extrusion die assembly and to a system for producing extruded products utilizing the die assembly, More particularly, the invention a free-standing, die detached from the extruder.
Extruders, of both the single screw and twin-screw types, are widely used in a number of industries, especially the food industry in which extruders are utilized to produce a variety of products such as snack foods, breakfast cereals, pet foods, texturized vegetable proteins, and confections. Typical extruders consist of one or more sets of flighted screws which rotate within a barrel. Suitable ingredients are introduced into the inlet end of the extruder, with the ingredients being cooked and formed into a flowable dough during passage through the extruder by dissipation of mechanical energy through shearing action, and/or heat transfer through jackets surrounding the barrel and/or by steam injection into the barrel. The flowable dough thus formed is forced through one or more die openings of uniform size and shape in a die plate mounted across the discharge end of the extruder, and the extrudate is cut into pieces of a desired length and dried.
Extrusion dies currently used in the production of extruded foods give rise to a number of disadvantages in commercial production operations. For example, since the die plate is mounted on the extruder head, the number of die openings in the die plate is limited by the diameter of the extruder head, thereby limiting the production capacity of the extruder. Moreover, the production of extruded pieces having different shapes requires the use of separate die plates, each having die orifices of one desired cross-sectional configuration, so that the operation of the extruder must be interrupted to effect such a change. If a single extruder is used, a predetermined quantity of extruded pieces having one shape/size is produced, after which, operation of the extruder is interrupted while the die plate is replaced with another having die orifices of a different shape/size. Such interruptions in the operation of the extruder has an adverse effect on the production capacity of the extruder.
In the production of coextruded foods, that is, products having an outer shell, such as an expanded, cellular farinaceous and/or proteinaceous material, surrounding a central core of material which is dissimilar in some respect (e.g. texture, composition, consistency, color, flavor, etc.) from the shell material, the shell and core materials typically are processed in separate extruders. The separate materials are then extruded through concentric dies in a die plate mounted across the discharge end of one of the extruders, generally the extruder in which the shell ingredients are processed. Typically the two extruders are positioned perpendicular to one another, with the discharge ends of the extruders abutting one another. This arrangement of the extruders and the concentric dies in the production of coextruded products is disadvantageous in a number of respects. For example, positioning the extruders so that the discharge ends abut one another restricts the placement options for the extruders. Moreover, the number of concentric dies in the die plate is limited by the diameter of the extruder head, thereby limiting production capacity of the coextrusion operation.